This invention relates to novel cyclic phosphazenes and phosphazene based functional fluid compositions.
A variety of phosphazene compositions and methods of preparation are known in the art. U.S. Pat. No. 3,291,865 to Kober, et al discloses non-flammable, hydrolytically stable phosphazene compositions for use as hydraulic fluids, lubricants and additives. These phosphazenes are substituted by an aryloxy and a polyfluoroalkoxy substituent, and are synthesized by forming the alkali metal salt of the fluorinated alkanol followed by reaction of the salt and a salt of a phenol with a phosphonitrilic chloride.
The alkoxy substituent may be any C.sub.2 to C.sub.21 polyfluoroalkoxy substituent. Examples of polyfluoro alcohols useful in providing this substituent include 1,1,3-tri-H-tetrafluoropropyl alcohol, 1,1,5-tri-H-octofluoropentyl alcohol, 1,1,7-tri-H-dodecafluoroheptyl alcohol, 1,1-di-H-trifluoroethyl alcohol, 1,1-di-H-heptaflurobutyl alcohol, 1,1-di-H-pentadecafluorooctyl alcohol and mixtures thereof. The aryloxy substituent may be derived from any of a variety of phenolic compounds, including monohydroxy phenols such as phenol and naphthol, phenoxyphenols, alkoxy-substituted phenols, alkyl-substituted phenols, aryl-substituted phenols, halogen-substituted phenols, halogen-alkyl-substituted phenols, and halogen-alkoxy-substituted phenols. Only phosphazene based compositions with one type of aryloxy substituent are exemplified. Similar phosphazene based compositions are described in the articles "Fluoroalkyl Phosphonitrilates: A New Class of Potential Fire-Resistant Hydraulic Fluids and Lubricants", H. Lederle, E. Kober and G. Ottmann, Journal of Chemical and Engineering Data, Volume 11, No. 2, April 1966; and "Fluoroalkyl Phosphonitrilates: A New Class of Potential Fire-Resistant Hydraulic Fluids and Lubricants", E. Kober, H. Lederle and G. Ottmann, ASLE Transactions 7, 389-397 (1964).
Polyfluoroalkoxy-substituted phosphazenes are disclosed in U.S. Pat. No. 3,304,350 to Kober, et al. Examples of useful polyfluoro alcohols include 1,1-di-H-trifluoroethyl alcohol, 1,1-di-H-pentafluoropropyl alcohol, 1,1-di-H-heptafluorobutyl alcohol, 1,1-di-H-pentadecafluorooctyl alcohol, 1,1,3-tri-H-tetrafluoropropyl alcohol and 1,1,5-tri-H-octafluoropentyl alcohol. A variety of other phosphazene compositions are known in the art. U.S. Pat. No. 3,370,020 to Allcock, et al, U.S. Pat. No. 3,505,087 to Godfrey, U.S. Pat. No. 4,081,593 to Lanier, U.S. Pat. No. 4,018,967 to Roller, et al, U.S. Pat. Nos. 4,110,421, 4,157,425 and 4,116,891 to Dieck, et al, U.S. published patent application No. B 369,221 to Kao, U.S. Pat. No. 3,990,900 to Franko Filipasic, et al and U.S. Pat. No. 3,545,942 to Rice, et al disclose phosphazenes which may be substituted by a variety of alkoxy, alkenyloxy, arylalkoxy or aryloxy groups.
However, many known phosphazene based compositions, such as those discussed above, have limitations which make them unsuitable for many functional fluid applications.
A functional fluid composition usually must demonstrate acceptable characteristics with regard to at least three properties; (1) fire resistance, (2) low temperature fluidity, and (3) compatibility with seal compositions. Failure of a functional fluid with respect to any of these properties may have serious consequences under the conditions of use.
In 1953 and 1954 the U.S. aircraft carriers "Leyte" and "Bennington", respectively, were heavily damaged due in part to explosions caused by flammable hydraulic fluids. Consequently, fire resistance is a critical characteristic for military, industrial or consumer applications. Unfortunately, adequate fire resistance is lacking for many phosphazene based compositions, particularly those wherein the functional groups are moieties which include unhalogenated, relatively large alkyl substituents.
However, phosphazene based compositions which exhibit good flame retardancy may also be solids under most conditions of use. This may make them unsuitable for certain applications, such as hydraulic fluids and lubricants, wherein liquidity may be required. Even if a phosphazene composition initially is a homogenous liquid, many phosphazene based compositions tend to completely or partially solidify or to separate into different phases after standing for a period of time. This tendency is particularly problematic for low temperature applications, such as outdoor hydraulic systems, wherein the functional fluid may be exposed to very low temperatures for prolonged periods of time. Such a tendency to solidify or undergo phase separation may make a composition unsuitable for certain uses, such as functional fluids in sealed hydraulic systems, wherein monitoring of the state of the phosphazene is impossible and replacement is impracticable.
Although certain phosphazene based compositions may remain liquid for a relatively long period of time, this liquidity may be due to impurities present in the composition, rather than to the characteristics of the composition per se. These impurities may cause degradation of the phosphazene compounds over a period of time or may corrode the apparatus with which the composition comes in contact, thereby contributing to failure of the system in which the composition is used.
Although certain phosphazene based fluids, such as those wherein the phosphazenes are functionalized by fluorinated phenoxy and/or fluorinated alkoxy moieties, may exhibit acceptable fire resistance, these compositions may be incompatible with elastomers and other materials used to form seals in hydraulic and other functional systems. Such incompatability may cause the seals to swell or shrink excessively, thereby causing system failure.
Price and supply are also considerations. Although a variety of alkoxy and aryloxy compounds may be used to form cyclophosphazene ester compositions, these compounds vary widely in cost and availability. It is therefore advantageous to be able to use relatively low cost and readily obtainable materials to synthesize a phosphazene based functional fluid composition having good fire resistance, low temperature fluidity and elastomer compatibility.